1. Field of the Invention
This invention relates to the controlled cooling of a hot particulate material and particularly a hot particulate carbon type material which must be cooled in order that it might be further handled and used. The invention is even more particularly concerned with the cooling of calcined "delayed" petroleum coke, i.e., petroleum coke which has been produced in a delayed coker before being calcined.
2. Description of the Prior Art
The invention will be described by specific reference to the processing of "delayed" petroleum coke, it being understood that its teachings are applicable to the processing of other hot particulate materials.
In the usual way of producing "delayed" calcined petroleum coke, the "raw" petroleum coke from the delayed coker is processed through a slightly inclined rotary kiln (typical dimensions of which might be 10 feet in diameter and 180 feet long) wherein it is heated to an elevated temperature such as 2000.degree.-2600.degree. F, which temperature causes a change in the volatile matter (VM) content of the coke from an initial VM typically between 8 and 20% to a final VM content of less than 1%.
Typically, the raw petroleum coke is removed from the delayed coker by the use of high pressure water jets. The action of these water jets generates some coke"fines." Also, in its passage through the long rotary kiln the coke is abraded some more due not only to the distance it travels and the rotation of the kiln, but due also to the typical use of "lifters" of modest height within the kiln which subject the coke particles in some measure to lifting-falling action during their passage through the kiln while they are being heated. This abrasion of the coke occurring in the kiln also generates some coke "fines" and also coke "dust."
After being heated in the kiln, the calcined coke is then cooled. In a typical commercial practice, this is done by transferring the coke directly into a long rotary cooler wherein it is exposed to water spray nozzles and air and wherein its temperature is reduced from its calcination temperature to a much lower exit temperature, at which it can be shipped or stored, such as 200.degree. F or lower. (A maximum temperature limitation of 130.degree.-150.degree. F on coke loaded into the holds of ships is a common requirement.) Such a cooling method has always given rise to problems in controlling the temperature of the coke and the residual water content of the product, as well as to pollution problems. These latter problems of pollution alone may require an expenditure of $200,000 to $300,000 per individual calciner-cooler commercial installation to overcome same.
In cooling the calcined coke to the desired degree in the rotary cooler, the calcined coke is also typically subjected to mechanical action similar to that which takes place in the rotary kiln. This also causes some size degradation of the particles as does the action of the water from the spray nozzles.
Thus the generation of "fines" and "dust" of relatively substantial magnitude has been, and is in current practices a "necessary evil" in order to make the desired calcined coke product, as it frequently is also in the production of particulate materials other than calcined coke.
As used herein, "fines" are defined as particles smaller than generally desired by the user or purchaser of the coke or other particulate product, and "dust" refers to particles so small that their presence can, for example, be ascertained simply by dropping a handful of the coke or other type particulate product upon a surface from a height of about two feet and observing a "cloud" of dust or particles separating from the general mass of the rest of the material landing upon the surface.
Such "fines" typically are of reduced economic value as compared to the rest of the calcined coke or other particulate type product; the "dust" not only has this disadvantage but also causes an air pollution problem, not only at the site of the calcined coke (or other type particulate material) manufacture but also at any final use location or shipment transfer point of the particulate product.